A substrate integrated waveguide technology is an innovative waveguide structure. Such a technology has risen in recent years and can be integrated into a dielectric substrate. The innovative waveguide structure has advantages of using both a planar transmission line and a metal waveguide. This type of structure is irreplaceable in microwave circuit design. With maturity and development of the substrate integrated waveguide technology, microwave devices such as filters, power splitters, and antennas can be implemented by using substrate integrated waveguide structures. In communications systems, a filter has a special purpose, function, and is essential. Conventional substrate integrated waveguide filter can have a relatively large structural size, and occupy a large area on a microwave board, which goes against miniature system design and structure. Additionally, conventional substrate integrated waveguide filters can have relatively poor out-of-band suppression performance and a relatively close parasitic passband (away from a primary passband by 2f0).
A conventional miniature substrate integrated waveguide resonator can structurally include an upper PCB board, a lower PCB board, and several plated through-holes. A first copper clad layer, a second copper clad layer, a first dielectric layer, and several internal plated through-holes can define an upper resonator. A third copper clad layer, a fourth copper clad layer, a second dielectric layer, and several internal plated through-holes can define a lower resonator. Each resonator can define a triangle, and copper clad surfaces that can be stacked and in contact with each other. The two resonators can be etched with metal slots to couple and cascade the upper resonator and the lower resonator into one resonator. Metal slots obtained through etching along directions of plated through-holes can define a triangle. For this type of conventional waveguide resonator, a planar area of a resonator can be reduced, but the planar area still has not reached its minimum size, which can be further reduced. Such a conventional resonator can have a parasitic passband of a filter formed relatively close to a primary passband (at a distance of 3f0, where f0 is a center frequency of the primary passband), and if the filter is used in a microwave circuit, a system signal-to-noise ratio can be deteriorated.
Furthermore, such conventional substrate integrated waveguide use a Chebyshev filter. The filter can be a directly coupled triangular substrate integrated waveguide cavity filter, including isosceles triangular cavities. The isosceles triangular cavities can be sequentially arranged into a regular polygon. Any two neighboring isosceles triangular cavities can be, respectively, a start cavity and an end cavity. An input port and an output port can be, respectively, disposed on the start cavity and the end cavity. A coupling window can be disposed between the start cavity and a cavity neighboring to the start cavity. A coupling window can be disposed between the end cavity and a cavity neighboring to the end cavity. The coupling window can be disposed between neighboring cavities, and the neighboring cavities can be located between the start end cavity and the end cavity. The isosceles triangular cavities can be formed by plated through-holes provided on a dielectric substrate having both surfaces covered with a metal foil, and the plated through-holes can be arranged into an isosceles triangle. The use of such a conventional filter has an excessively large size in which aspects of an area and size are not improved. Such a conventional cavity filter also can have parasitic passband relatively close to a primary passband (at a distance of 2f0, where f0 is a center frequency of the primary passband), and out-of-band suppression can be insufficient. That is, such a conventional Chebyshev filter has a single magnetic coupling form used between filter units of the filter in which out-of-band suppression of the filter is not high.